The liver

The liver is part of the digestive system. It is the largest solid organ in the body. In adults, the liver can weigh up to 1.5 kg. It is in the upper-right abdomen, just under the rib cage and below the diaphragm (the thin muscle below the lungs and heart that separates the chest cavity from the abdomen).

Structure

The liver has 2 main lobes. The right lobe is larger than the left lobe. Each lobe is divided into segments.

The lobes are separated by a band of tissue called the falciform ligament (also called the broad ligament). This ligament also attaches the liver to the diaphragm.

A layer of connective tissue, called Glisson’s capsule or the capsule, covers the liver.

Blood vessels

Unlike most other organs, the liver has 2 major sources of blood:

The portal vein carries blood from the digestive system, which removes most of the oxygen in the blood, to the liver. About 75% of the liver’s blood supply comes from the portal vein. This blood has nutrients from the digestive system.

The hepatic artery supplies the liver with oxygen-rich blood from the heart.

Most of the blood is removed from the liver through the right, middle and left hepatic veins.

Bile ducts

Liver cells (called hepatocytes) make bile. Bile is a yellow-green fluid that helps the body digest fat. Bile travels through a series of tubes, or ducts, in the liver to the small intestine or to the gallbladder for storage.

The hepatic ducts collect bile from the liver. Two hepatic ducts leave the liver and join to form the common hepatic duct.

The cystic bile duct leaves the gallbladder and joins the common hepatic duct to form the common bile duct.

The common bile duct empties bile into the duodenum (the first part of the small intestine).

If there is food in the small intestine, the bile will flow directly from the liver, through the common hepatic duct and common bile duct into the duodenum to help with digestion.

If the small intestine is empty, the bile will collect in the common bile duct until it backs up into the cystic duct and into the gallbladder, where it is stored until it is needed.

Function

The liver makes bile. Bile is made up of bile salts, cholesterol, bilirubin, electrolytes and water. Bile helps the small intestine digest and absorb fats. It also helps the small intestine absorb cholesterol and some vitamins. Bile breaks down fat from food to make it easier to digest.

The body also needs bile to absorb vitamin K. The body uses vitamin K to make blood-clotting, or coagulation, factors. If the liver doesn’t make enough bile, the body will absorb less vitamin K and make less blood-clotting factors.

Liver enzymes break down proteins from food so they can be digested and used by the body.

The liver absorbs and uses, or metabolizes, bilirubin. Bilirubin is a yellow-red substance formed from hemoglobin when red blood cells (RBCs) break down. Hemoglobin is a protein found in RBCs that carries oxygen and gives blood its red colour. The iron from the hemoglobin is stored in the liver or used by the bone marrow to produce new RBCs.

The liver helps the body metabolize carbohydrates. The body breaks down carbohydrates from food into glycogen, which is stored in the liver. The liver breaks down glycogen into glucose and releases it into the blood to maintain normal blood sugar levels.

The liver stores vitamin A, D, E, K and B12. It also stores iron in the form of ferritin, which it releases so the body can make new RBCs. The liver stores and releases copper as needed.

The liver filters certain substances from the blood so that they don’t build up and cause damage. Substances that come from within the body include hormones, such as estrogen, aldosterone and anit-diuretic hormone. Substances that come from outside the body include alcohol and other drugs, such as amphetamines, barbiturates and steroids.

Regeneration

The liver has the unique ability to regrow parts that have been removed so that it can continue to function in the body. If part of the liver is removed, it will regenerate for several months until the missing liver tissue is replaced. How long it takes the liver to regenerate depends on your age and nutrition, if there is any liver damage and how much liver was removed. Your liver can still function even when a large part of it has been removed.